The most popular spread spectrum modulation techniques for use in wireless communication systems are direct sequence (DS) and frequency hopping (FH). Depending upon the system requirements, each modulation has its set of advantages and disadvantages. In a messaging environment, frequency hopping is more attractive than direct sequence because it requires no power control at a portable subscriber unit. Direct sequence is more attractive for location finding applications (using time of arrival (TOA) or where spectral reconstruction can be used in interference cancellation scenarios.
In general, by optimizing the system toward a given application, performance is lost in other applications. For example, a system optimized for location finding will typically degrade applications for long messaging. As the messaging market grows, more and more applications are being supported by the same system (network, subscriber unit and base receiver). Thus, a need exists for a hybrid system using a combination of spread spectrum techniques that optimizes performance for each type of application.